Urban agriculture's carbon footprint is 6x greater than normal farms

A recent study led by the University of Michigan dove into the world of urban agriculture, uncovering fascinating insights about its impact on the environment.

This comprehensive study, the largest of its kind, juxtaposes the carbon footprint of urban-grown fruits and vegetables with their conventionally grown counterparts.

Environmental footprint of city-grown produce

The study, involving 73 urban farms and gardens across five countries, reveals a complex picture.

On average, urban-grown produce has a carbon footprint six times larger than conventionally grown fruits and vegetables.

This is a significant finding, considering the growing popularity of urban agriculture worldwide.

An estimated 20% to 30% of urban dwellers globally engage in some form of city farming, making these findings particularly relevant.

However, the study also highlights intriguing exceptions. Certain crops, like tomatoes cultivated in open-air urban plots, have a lower carbon intensity compared to those grown in conventional greenhouses.

Additionally, the carbon emissions gap between conventional and urban agriculture narrows for crops typically air-freighted, such as asparagus.

Urban agriculture has low-carbon potential

Jason Hawes, a doctoral student at the University of Michigan’s School for Environment and Sustainability and co-lead author of the study, emphasizes the potential for urban agriculture to reduce its climate impacts.

“The exceptions revealed by our study suggest that urban agriculture practitioners can reduce their climate impacts by cultivating crops that are typically greenhouse-grown or air-freighted, in addition to making changes in site design and management,” he explains.

This approach not only benefits the climate but also the communities and the very essence of sustainable urban living.

Urban agriculture isn’t just about food production. It’s a multifaceted practice that offers a myriad of social, nutritional, and localized environmental benefits.

“Urban agriculture offers a variety of social, nutritional and place-based environmental benefits, which make it an appealing feature of future sustainable cities,” Hawes said.

“This work shines light on ways to ensure that urban agriculture benefits the climate, as well as the people and places it serves.”

Carbon contrast: Urban vs. conventional agriculture

The study meticulously compared the carbon footprints of low-tech urban agriculture sites with those of conventional crops.

This comparison involved urban farms (professionally managed for food production), individual gardens (small plots tended by a single gardener), and collective gardens (communal spaces managed by groups).

Researchers calculated the greenhouse gas emissions associated with each site’s materials and activities over its lifetime.

Their findings are telling: urban agriculture emits an average of 0.42 kilograms of carbon dioxide equivalents per serving of produce, a stark contrast to the 0.07 kg CO2e per serving from conventional methods.

“By assessing actual inputs and outputs on urban agriculture sites, we were able to assign climate change impacts to each serving of produce,” notes Benjamin Goldstein, assistant professor at U-M’s School for Environment and Sustainability and co-lead author of the study.

“This dataset reveals that urban agriculture has higher carbon emissions per serving of fruit or vegetable than conventional agriculture — with a few exceptions.”

Composition of urban agriculture

Urban farming sites are typically characterized by three key elements: infrastructure (such as raised beds and pathways), supplies (like compost, fertilizers, and gasoline for machinery), and irrigation water.

These components form the backbone of any urban farm but also contribute significantly to its overall carbon impact.

Goldstein highlights a critical point, saying, “Most of the climate impacts at urban farms are driven by the materials used to construct them — the infrastructure.”

He points out that the limited operational lifespan of these farms, often just a few years or a decade, means that the greenhouse gases emitted to produce these materials are not utilized effectively.

“These farms typically only operate for a few years or a decade, so the greenhouse gases used to produce those materials are not used effectively. Conventional agriculture, on the other hand, is very efficient and hard to compete with,” Goldstein concluded.

This inefficiency contrasts sharply with conventional agriculture, which tends to be more efficient and harder to compete with in terms of carbon footprint.

In conventional farming, practices like mono-cropping, aided by pesticides and fertilizers, lead to larger harvests and, as a result, a smaller carbon footprint per unit of produce when compared to urban farming.

Making urban farming carbon-efficient

The study outlines three best practices to enhance the carbon competitiveness of low-tech urban agriculture:

Extending Infrastructure Lifetimes: Prolonging the use of urban agriculture materials and structures, such as raised beds and composting infrastructure, can significantly reduce their environmental impact per serving of food. For instance, a raised bed used for 20 years will have a quarter of the impact of one used for just five years.

Utilizing Urban Wastes: Adopting “urban symbiosis” can conserve carbon by repurposing used materials like construction debris for urban agriculture. This approach also includes using rainwater and recycled grey water for irrigation, thereby reducing the carbon footprint.

Maximizing Social Benefits: The study underscores the non-environmental advantages of urban farming, noting improvements in mental health, diet, and social networks among UA farmers and gardeners. While these benefits don’t directly reduce carbon emissions, they contribute to the holistic appeal of urban agriculture, potentially making it more competitive with conventional farming.

International collaboration and insights

In summary, while urban farming currently faces challenges in terms of its carbon footprint, this study provides actionable insights and strategies to mitigate these impacts.

By extending the life of infrastructure, creatively reusing urban waste, and enhancing social benefits, urban agriculture can evolve into a more sustainable and competitive alternative to conventional farming.

This expansive study was a collaborative effort led by Joshua Newell, professor and co-director of the Center for Sustainable Systems at U-M’s School for Environment and Sustainability.

The team consisted of international collaborators from universities near the urban farming sites, and farmers and gardeners in France, Germany, Poland, the United Kingdom, and the United States contributed as citizen scientists.

Their dedication to recording daily inputs and harvests throughout the 2019 season provided an invaluable dataset.

The team’s research expands our understanding of urban agriculture’s environmental footprint but also guides future practices towards sustainability.

As cities continue to grow and evolve, incorporating climate-friendly urban farming practices becomes increasingly vital for a sustainable future.

The full study was published in the journal Nature Cities.

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